Downhole shut-in device for pressure variation testing in gas lift wells

ABSTRACT

The device is based on the principle of downhole shut-in of oil producing wells that do not flow to surface self-powered but require the injection of gas to lighten the fluid column and thus enable the well to produce. This downhole shut-in device comprises a check valve, an anchoring system, a seal system; an untethering system, a shock absorber and a sleeve for the protection of pressure and temperature memory probes. 
     The objective of the downhole shut-in device is to obtain characteristic information of the fluid-rock system from variations in the pressures recorded in order to obtain the dynamic characterization of the reservoir.

FIELD OF THE INVENTION

The present invention relates to a downhole shut-in device for testing pressure variation in gas lift wells. These wells require high pressure gas injection in order to decrease the hydrostatic column weight, since without pressure power oil ceases flowing. Thus, this downhole shut-in device, object of the invention, is capable of testing pressure variation in gas lift wells. Currently it has no precedent in the national and international market. This invention is used in the area of field exploitation.

BACKGROUND OF THE INVENTION

According to the history of the country's hydrocarbon production, in recent years we have observed that oil production has been declining. To stop this we require development and/or improvement of current techniques specifically focused on oil extraction. Exploitation of mature fields or low pressure ones requires generating strategies to incorporate new technologies and design scenarios, planning, operation, maintenance, monitoring, control and optimization of production systems throughout the production life. Therefore, there is the need for the use of advanced technologies for the acquisition of downhole information. One technique for acquiring such information is the pressure variation testing.

Pressure variation tests are to generate and record pressure variation downhole of one or more wells for a period of time. These downhole pressure variations are generated by modifying injection or production conditions of the wells.

The purpose of testing pressure variations is to obtain characteristic information from the fluid-rock system (petrophysical properties of the reservoir). From the pressure variations recorded, we can obtain the dynamic characterization of the reservoir in order to establish the optimum exploitation system.

Techniques for generating pressure disturbance are based primarily on surface operations such as opening and /or closing the well, fluid injection, variation in throttle, etc. The echometer is the device that collects information in this type of operation. When performing these surface operations there arise technical-mechanic issues, undesired physical phenomena, impacts to surface facilities, among others. These problems affect the quality of information and cannot be filtered by the echometer, reducing then the reliability of the same. The shortcomings of the echometer are that production rigging must not present accessories that alter the behavior of the sound wave, and it is only applied in liquid wells.

Therefore, the Systems and Tools for Information Acquisition from Wells (SHAIP for its acronym in Spanish) group of the Instituto Mexicano del Petróleo (Mexican Petroleum Institute), set itself the task of developing a device that can generate pressure disturbances inside a gas injection well comprising the following characteristics: installation close to the producing reservoir; use in wells with gas present; diminishing or eliminating storage effects of the well with short times of interruption of production; not being affected by rigging accessories of production; and that the recorded information be reliable. Based on these characteristics, we obtain the downhole shut-in device for pressure variation testing in gas lift wells.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to provide a clear and accurate description of the functionality of the downhole shut-in device of the present invention, reference is made to the accompanying figures.

FIG. 1 shows the general components of the downhole shut-in device for pressure variation testing in gas lift wells.

FIG. 2 shows the typical curve obtained by processing the information retrieved from the downhole shut-in device.

FIG. 3 shows the plotted results of the pressure variation test obtained in Well Coyotes 461 of PEMEX.

DETAILED DESCRIPTION OF THE INVENTION

Below is a detailed description of our invention, for which reference is made to the accompanying descriptive figures.

FIG. 1 shows the device, object of the invention, which is constituted by a retaining pressure check valve with variable opening (1), which permits passage of the flow in the reservoir; an anchoring system (2) that installs the device inside the production tubing, a sealing system (3) which serves to seal the wellbore; untethering system (4), to retrieve the device, a shock absorber (5), which has the function of dissipating the energy generated by shock and vibration in the device body, through all stages of the operation, which can damage the memory probe set pressure and temperature, and a jacket for the memory probes (6) to prevent loss of information because the operating conditions in the reservoir, avoiding also damages to probe circuitry. This downhole shut-in device for testing pressure variation in gas lift wells is placed downstream of the operation valve, just at the lower end of the production tubing, and is mainly used to generate pressure variations in gas lift wells through a pressure check valve with variable opening, which allows only the flow from below upwards of the closing equipment and opens when the differential pressure (lower initial pressure and higher flow pressure) is greater on magnitude than the calibration pressure of the valve after opening the well and injecting the gas for pneumatic pumping.

The present invention is based on the principle of downhole shut-in of oil producing wells that do not flow to the surface self-powered, but require the injection of gas to lighten the fluid column and thus enable the well to produce. At the beginning, only the fluids into the production tubing will be moved with pneumatic gas injection pumping until the differential pressure between the inferior initial pressure (P1 initial) and the superior pressure due to flow (P2 flow) is greater on magnitude than the calibration pressure of the valve (P3 spring), the pressure check valve with variable opening (FIG. 1) which will open and begin the drawdown pressure stage in downhole (FIG. 2).

P₃ Spring<PInitial−P₂ Flow

After closing the well and stopping the pneumatic gas injection pumping, the downhole pressure will seek to achieve the pressure P1 initial and the flow will increase to fulfill the following inequality for the check valve closure:

P ₃ spring<P ₁flow−P ₂ flow

Once the valve is closed, downhole pressure increment will start due to the reservoir response without the effects of the fluid stored in the well (FIG. 2).

The present invention operates by downhole shut-in to minimize storage effect within the well and duration of the variation pressure tests.

Operation of the Parts Constituting the Invention

-   1. Check Valve:

Non-return or check valve with variable opening that will isolate the bottom of the well as this area does not have a high enough pressure to overcome the pressure of the upper zone; it has a fluid homogeneous inlet and outlet according to the fluid composition, flow velocity and downhole pressure when well is flowing. At the top has a fishing neck, which is designed to work with JDC type pulling tool.

-   2. Anchorage System:

Bidirectional anchoring system comprises four lower jaws and three upper ones that allow the device to be placed on any free area of the production tubing. The system is activated by falling impacts.

-   3. Seal System:

This system comprises three seals made of high-strength polymer to the temperature and chemical attack. These seals insulate the top of the lower zone of the well to ensure the flow path through the interior of the device. Actuation occurs when the falling impacts activate the anchoring system, whereupon compression occurs on the seals, so that they reduce theft length and increase theft diameter.

-   4. Untethering System:

Untethering system comprises bolts made of high tensile strength but low shear strength. Its function is to maintain the anchorage of the tool until the time to be retrieved upon.

-   5. Shock Absorber:

The shock absorber has the function of dissipating the energy generated by shock and vibrations in the body of the device during all stages of the operation, which can damage the memory probe set. Its principle is based on the combination of the spring-damper.

-   6. Probes Jackets,

Produced in high strength steel, they will have the purpose of protecting memory probes from any impact effects occurring during development of the device operation.

EXAMPLES Application in Well Coyotes 461 PEMEX.

The results obtained in the pressure variation test in Well Coyotes 461 made with the “downhole shut-in device for testing pressure variation in aft lift wells IMP” and high resolution memory probes at 955 m depth are presented. The shut-in period was carried out with downhole shut-in, allowing a clear definition of the response of a hydraulically fractured well and we were able to identify the different flow periods in a Reservoir-Hydraulic Fracture-Well system.

Well Coyotes-461 produces at an interval of 993 to 1040 m, that belongs to the body of sand Sim_(—)50, of Chicontepec formation. The well is located in the central part of the field Coyotes. It is located NW of Paleocanal Chicontepec within the study area called Sector 3.

Analysis determined that the well has a finite conductivity fracture with a length of 88 m, which represent 61% of the programmed (144 m) and a conductivity of 10.4×10⁻³ Darcy/ft which is well below of estimated (2855 mD-ft) by Byron Jackson Company (BJ).

The well was producing with a rate of 16-20 bpd and a head pressure of 4-6 kg/cm2. Based on this, we asked the production area of Activo Cerro Azul, belonging to Poza Rica-Altamira, a portable separator installed to measure the volume of gas and liquid before closing the well, With the well closed, and using slickline the well was calibrated with a printing block of 2 5/16 going down “free” to 1060 m, subsequently the accessory “collar stop” was descended and anchored at 960 m.

Two pressure and temperature high resolution probes were programmed and the device of downhole shut-in was assembled with check valve and the two probes connected to their respective battery. The trial period took place after starting the pneumatic gas injection pumping, producing gas and liquid toward liquids dam and subsequently carry it to portable separator for measurement.

Once the probe was retrieved and pressure information obtained, we proceeded to perform the analysis. FIG. 3 shows the total time spent on the test of pressure variation (pressure trend, pressure increase curve and decrease curve). The buildup test shows a trend fairly good, almost perfect, without distortion or abnormalities during development. This is because the downhole shut-in was effective and there was no leakage through the seals and the interior of the check valve calibrated to ⅓ of downhole pressure. The literature mentions that the buildup curves are the most representative due to full control of the flow rate because the well is closed, so that the flow rate is zero as long as there are no leaks.

From This Test it was Concluded That:

A.) The drawdown pressure was successfully performed by the lightening of the hydrostatic column, through the gas injection through the annular space and the corresponding opening of the check valve calibrated previously

B) The shut-in downhole, which was conducted stopping the gas injection through the annular space and the corresponding closure of the precalibrated check valve. Through buildup test, which allowed reducing storage effects, it have gotten a clear definition of the response of a finite conductivity in a “Reservoir-hydraulic fracture-Well” system. 

1. A downhole shut-in device for testing pressure variation in gas lift wells, characterized in that it comprises a check valve for pressure retaining with variable opening, which allows the flow path of the reservoir, an anchoring system, which allows to install the device into the production tubing, a sealing system which has the function of sealing the well, an anchorage system, which is composed of four lower jaws and three upper ones; an untethering system, which allows to retrieve the device, a shock absorber, which serves to dissipate the energy generated by shock and vibration in the body of the device during all stages of the operation and a jacket for memory probes, to avoid loss of information due to operating conditions in which the reservoir may be, even preventing damage to probe circuitry.
 2. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the check valve allows reservoir flow only from bottom to top of the closure equipment.
 3. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the check valve has a homogeneous fluid inlet and outlet according to the fluid composition, flow rate and downhole pressure when the well is flowing, and at the top it has the fishing neck, which is designed to work with a JDC pulling tool.
 4. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the anchorage bidirectional system comprises four lower jaws and three upper ones, which allow the device to be placed on any free area of the production tubing.
 5. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the sealing mechanism comprises three high temperature resistant seals and ensures the tightness to prevent the well flow pass otherwise than within the device in its operation.
 6. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the shock absorber can dissipate the energy generated by shock and vibration in the device body during all phases of operation.
 7. A downhole shut-in device for testing pressure variation in gas lift wells, according to claim 1, wherein the probe jacket protects memory probes from any impact occurred during the course of the operation of the device. 